Biofouling and Biofilm Processes Section, WSCD, Chemistry Group, Bhabha Atomic Research Centre, Kalpakkam, 603102, India.
Homi Bhabha National Institute, BARC Training School Complex, Anushaktinagar, Mumbai, 400094, India.
World J Microbiol Biotechnol. 2024 Apr 17;40(6):165. doi: 10.1007/s11274-024-03982-4.
Bacterial reduction of hexavalent chromium (VI) to chromium (III) is a sustainable bioremediation approach. However, the Cr(VI) containing wastewaters are often characterized with complex conditions such as high salt, alkaline pH and heavy metals which severely impact the growth and Cr(VI) reduction potential of microorganisms. This study investigated Cr(VI) reduction under complex haloalkaline conditions by an Alteromonas sp. ORB2 isolated from aerobic granular sludge cultivated from the seawater-microbiome. Optimum growth of Alteromonas sp. ORB2 was observed under haloalkaline conditions at 3.5-9.5% NaCl and pH 7-11. The bacterial growth in normal culture conditions (3.5% NaCl; pH 7.6) was not inhibited by 100 mg/l Cr(VI)/ As(V)/ Pb(II), 50 mg/l Cu(II) or 5 mg/l Cd(II). Near complete reduction of 100 mg/l Cr(VI) was achieved within 24 h at 3.5-7.5% NaCl and pH 8-11. Cr(VI) reduction by Alteromonas sp. ORB2 was not inhibited by 100 mg/L As(V), 100 mg/L Pb(II), 50 mg/L Cu(II) or 5 mg/L Cd(II). The bacterial cells grew in the medium with 100 mg/l Cr(VI) contained lower esterase activity and higher reactive oxygen species levels indicating toxicity and oxidative stress. In-spite of toxicity, the cells grew and reduced 100 mg/l Cr(VI) completely within 24 h. Cr(VI) removal from the medium was driven by bacterial reduction to Cr(III) which remained in the complex medium. Cr(VI) reduction was strongly linked to aerobic growth of Alteromonas sp. The Cr(VI) reductase activity of cytosolic protein fraction was pronounced by supplementing with NADPH in vitro assays. This study demonstrated a growth-dependent aerobic Cr(VI) reduction by Alteromonas sp. ORB2 under complex haloalkaline conditions akin to wastewaters.
六价铬（VI）还原为三价铬（III）是一种可持续的生物修复方法。然而，含有六价铬的废水通常具有复杂的条件，如高盐度、碱性 pH 值和重金属，这些条件严重影响微生物的生长和六价铬的还原潜力。本研究通过从海水微生物组中培养的好氧颗粒污泥中分离出的耐盐菌属 ORB2 研究了在复杂的盐碱性条件下的六价铬还原。耐盐菌属 ORB2 在 3.5-9.5%NaCl 和 pH7-11 的盐碱性条件下观察到最佳生长。在正常培养条件（3.5%NaCl；pH7.6）下，细菌生长不受 100mg/lCr(VI)/As(V)/Pb(II)、50mg/lCu(II)或 5mg/lCd(II)的抑制。在 3.5-7.5%NaCl 和 pH8-11 下，近 100mg/lCr(VI)在 24h 内完全还原。耐盐菌属 ORB2 对 100mg/LAs(V)、100mg/LPb(II)、50mg/LCu(II)或 5mg/LCd(II)的还原没有抑制作用。在含有 100mg/lCr(VI)的培养基中，细菌细胞的酯酶活性降低，活性氧水平升高，表明毒性和氧化应激。尽管存在毒性，但细胞在 24 小时内生长并完全还原了 100mg/lCr(VI)。培养基中 Cr(VI)的去除是由细菌还原为三价铬（III）驱动的，三价铬（III）仍留在复杂的培养基中。Cr(VI)的还原与耐盐菌属 ORB2 的好氧生长密切相关。在体外试验中，通过补充 NADPH，细胞质蛋白部分的 Cr(VI)还原酶活性显著。本研究表明，耐盐菌属 ORB2 在类似于废水的复杂盐碱性条件下，通过有氧生长依赖的方式还原六价铬。
